1. Field of the Invention
The present invention relates to synergistic antimicrobial compositions which are generally useful for inhibiting microbial growth wherever such microbial growth is found, for example in aqueous systems related to a wide variety of industrial applications. More particularly, the present invention relates to synergistic admixtures of N-decyl-N-isononyl-N,N-dimethyl ammonium chloride and 2-bromo-2-nitropropane-1,3,-diol. Methods for using the same are also disclosed.
2. Description of the Background Art
Both N-decyl-N-isononyl-N,N-dimethyl ammonium chloride, referred to herein as N-DIDAC, and 2-bromo-2-nitropropane-1,3,-diol (BNPD), are known individually as antimicrobial agents. The unexpected finding of the present invention is that they are synergistic when used in combination. As used herein, the terms "synergy" and "synergistic" refer to instances where the effectiveness of a composition comprising two or more biocides, such as N-DIDAC and BNPD, exceeds the sum of the efficacies of the individual components taken alone. Thus, using a synergistic biocidal combination may allow for use of a lower overall concentration of biocide or the realization of an enhanced antimicrobial effect at a comparable dosage.
The use of 2-bromo-2-nitropropane-1,3-diol (BNPD) and related compounds is known in the art, both alone and in conjunction with other compounds. U.S. Pat. No. 5,292,776 discloses a synergistic admixture of diiodomethyl-p-tolylsulphone and 2-bromo-2-nitropropane-1,3-diol (BNPD) for fungal growth control in aqueous systems. U.S. Pat. No. 5,266,217 discloses a method of controlling growth of microorganisms in aqueous systems comprising polyvinyl alcohols and gallic or boric acid in combination with additional biocidal components such as an isothiazoline compound or a quaternary ammonium halide salt and BNPD. U.S. Pat. No. 5,112,871 discloses the use of bromonitro compounds other than BNPD as antimicrobial agents. U.S. Pat. No. 5,385,605 discloses synergistic antimicrobial compositions and methods for using the same comprising methylene (bisthiocyanate) and BNPD. U.S. Pat. No. 4,725,624 discloses synergistic antimicrobial compositions of BNPD and N-alkyl dimethyl benzyl ammonium chloride and methods of using the same.
Likewise, the use of N-decyl-N-isononyl-N,N-dimethyl ammonium chloride and related compounds is known. The synergistic combination of N-DIDAC and BNPD, however, is not taught or suggested in the art.
As used herein, the phrases "antimicrobial", "biocide", and "inhibiting microbial growth" refer to the killing of, the inhibition of, or the control of the growth of bacteria, yeast, mold and/or algae. A number of important industries have experienced serious adverse effects from the activity of such biological growth on the raw materials which they employ, in their process waters, on various components of their manufacturing processes, and in the finished products which they produce. Such industries include the paint, wood, textile, cosmetic, leather, tobacco, fur, rope, paper, pulp, plastics, fuel, oil, rubber, and machine industries.
It is contemplated that the synergistic admixture of N-DIDAC and BNPD as disclosed herein, and the methods for using the same, will be useful in virtually any aqueous system or on any article or product of manufacture in which inhibition of microbial growth is desired, absent compatibility problems. Suggested applications of the synergistic antimicrobial combinations of the present invention include, for example: inhibiting the growth of bacteria and fungi in aqueous paints, adhesives, latex emulsions, inks and joint cements; preserving wood; preserving cutting oils and metal working fluids; controlling slime-producing bacteria and fungi, including yeast and mold, in pulp and paper mills and cooling towers; as a spray or dip treatment for textiles and leather to prevent mold growth; as a component of anti-fouling paints to prevent adherence of fouling organisms; protecting paint films, especially exterior paints, from attack by fungi which occurs during weathering of the paint film; protecting processing equipment from slime deposits during manufacture of cane and beet sugar, food, foodstuffs and food additives; preventing microorganism buildup and deposits in air washer or scrubber systems and in industrial fresh water supply systems; controlling microorganism contamination in closed loop and recirculating water cooling systems; controlling microorganism contamination and deposits in oil field drilling fluids and muds, and in secondary petroleum recovery processes; preventing bacterial and fungal growth in paper coating processes which might adversely affect the quality of the paper coating; controlling bacterial and fungal growth and deposits during the manufacture of various specialty boards, e.g., cardboard, particle board and foodgrade board; preventing sap stain discoloration on freshly cut wood of various kinds; controlling bacterial and fungal growth in clay and pigment slurries of various types which are manufactured for later use in paper coating and paint manufacturing and which are susceptible to degradation by microorganisms during storage and transport; as a hard surface disinfectant to prevent growth of bacteria and fungi on walls, floors, etc.; in swimming pools to prevent algal growth; and to control bacterial and fungal growth in various cosmetic products. It is further contemplated that the synergistic admixture of the present invention will be useful in various types of non-aqueous systems as well.
The synergistic antimicrobial composition disclosed in the present invention is particularly applicable to slime control in papermaking processes. The control of bacteria and fungi in pulp and paper mill water systems which contain aqueous dispersions of papermaking fibers in various consistencies is especially important. The uncontrolled buildup of slime produced by the accumulation of bacteria and fungi may cause off-grade production, decreased production due to down-time and greater cleanup frequency, increased raw material usage, and increased maintenance costs. The problem of slime deposits is especially critical in light of the widespread use of closed white water systems in the paper industry.
Another important area in which the antimicrobial compositions of the present invention are particularly useful is in the control of bacterial and fungal growth in clay and pigment slurries. These slurries comprise various clays (e.g., kaolin) and pigments (e.g., calcium carbonate and titanium dioxide) and usually are manufactured at a location separate from the end use application. This means that they are generally transported and stored for later use at the application site. Because of high quality standards for the paper and paint products in which such slurries are used, it is essential that these clay or pigment slurries have a very low microorganism count.
In addition, the synergistic combination of the present invention and methods of using the same have been found especially useful in controlling the harmful effects of microorganisms in water or aqueous media. Systems which utilize circulating water or aqueous media become infected with microorganisms and experience substantial impairment of their efficiency when deposits of the microorganisms build up in the system. The deposits coat the walls of tanks and other vessels and any machinery or processing equipment which is employed and create blockages in pipes and valves. The deposits also create discolorations and other imperfections in the products being produced, forcing costly shutdowns. Control of microorganisms in aqueous media is particularly important where there are dispersed particles or fines in the aqueous media, for example, dispersed cellulosic fibers and dispersed fillers and pigments in papermaking, and dispersed pigments in paint manufacture.
Accordingly, there remains a very real and substantial need for antimicrobial compositions capable of effectively controlling and/or inhibiting microbial growth in industrial aqueous systems and on articles of manufacture. Because of increasing environmental regulations, there is still a further need to provide biocidal compositions having enhanced antimicrobial effect which are effective in lower doses than historically used. Use of lower amounts of biocides has a favorable impact on the environment, and allows users to realize significant cost savings.